In order to investigate the optimal UVB (ultraviolet B) treatment conditions for vitamin D2 enhancement of freeze-dried ear mushroom, sample size (below 300 μm~whole), UV treatment temperature (30~60℃), treatment density (6.25~50.0 mg/cm2) and the samples mixing frequency (1~32 times) were treated differently. After that, chromaticity, vitamin D2 and ergosterol (vitamin D2 precursor) contents were investigated. As a result of the investigating, effective UVB treatment conditions for vitamin D2 enhancement are as follows. The sample sizes were 2~4 mm and finely crushed pieces. The treatment temperatures were 50℃ and 60℃. The treatment density was 12.5 to 25.0 mg/cm2, and the number of sample mixing was 8 times or more. As the amount of vitamin D2 increased by UVB treatment, the ergosterol content generally tended to decrease. However, under some UVB treatment conditions, the vitamin D2 content was not high despite the decrease of ergosterol content. Under the conditions set in this experiment, it was possible to obtain ear mushrooms with enhanced vitamin D2 up to 26,968.7 μg/100 g. Therefore, it is thought that the ear mushroom is highly likely to be used as a vitamin D source and nutritionally fortified food ingredient.

To examine the possibility of ear mushroom (EM) as a source of natural vitamin D, the UVB (ultraviolet B) was treated according to sample drying status, drying methods before UVB treatment and harvest time. And then, vitamin D2 and ergosterol contents were investigated. According to the sample drying status, the vitamin D2 contents of fresh and freeze-dried EM (whole) increased to 4,634.4~4,780.9 μg/100 g D.W. (dry weight) under UVB dose 52.5~70.0 kJ/m2 and above 18,693.1 μg/100 g D.W. under above 105 kJ/m2, respectively. By drying methods before UVB treatment, vitamin D2 contents of EM powder (below 500 μm) that dried in the vinyl house and freeze-dryer increased to 4,886.2~5,132.9 μg/100 g D.W. under above 105 kJ/m2 and 17,103.7 μg/100 g D.W. under 70 kJ/m2, respectively. Ergosterol content decreased with increasing UVB dose in all experiments. According to the harvest time, vitamin D2 content under UVB dose 210 kJ/m2 showed marked difference and in order of June, July, August, October and April. As for the results, the optimum harvest time, drying method before UVB treatment, sample size, UVB dose for the EM contained high vitamin D2 content were June, freeze-drying, whole, and 105 kJ/m2, respectively.